The existing surge protection device is mainly composed of single varistor or a plurality of varistors. The existing ZnO varistor (Metal Oxide Varistors, MOV) has specific nonlinear current-voltage characteristic. The voltage and current variation region of a typical varistor is divided into three regions comprising cut-off region, break-over region and overload degradation region. If unusual situation occurs during use, for example being struck by lightning, suffering interference from electromagnetic field, the power supply is turning on/off frequently, or faults occurring in power system, the varistor will enter the break-over region due to the sudden increase of the voltage in the line that exceeds the break-over voltage of varistor. At this point, current (I) has a nonlinear relationship with voltage (V), which is called nonlinearity parameter and may be up to dozens or hundreds. In this case, the impedance of varistor reduces to only a few Ohms. The overvoltage produces surge current to flow out, whereby protecting all connected electronic products and expensive components.
In routine techniques, though varistor composed of ZnO chip has good protective effect on transient surge, it cannot protect the power system from transient overvoltage, or even resulting in fire. Thus it is standard choice to cut off the circuit or go off the grid. To this end, thermal fuse and current fuse are also usually used in the device in addition to switches.
However, due to its planar rectangle or planar circular shape, traditional surge protection device has a disadvantage of big occupied space in use that cannot meet the requirements of electronics securitization, miniaturization and inexpensiveness.